1. Field of the Invention
The present invention relates to a layout structure of a MOS transistor, and more particularly, to a layout structure of a power MOS transistor.
2. Description of the Related Art
A power MOS transistor is a particular kind of MOS transistor that is used as a dedicated component providing and switching power to integrated circuits. Accordingly, power MOS transistors require the capability to operate under high voltage. Typical power MOS transistors manufactured by CMOS process are of large size so as to be able to operate under high voltage. In addition, power MOS transistors also require the capability to provide a large output current. Therefore, in a typical manufacturing process, a power MOS transistor is composed of thousands to hundreds of thousands of transistor units, wherein each transistor unit can provide a small amount of output current. As a result, the power MOS transistor can provide a large output current.
FIG. 1 shows a conventional layout structure of a power MOS transistor. As shown in FIG. 1, the power MOS transistor 100 comprises a transistor unit 110. The transistor unit 110 comprises a source area 120, a gate area 130, a drain area 140 and a body area 150. Both the drain area 140 and the body area 150 exhibit a rectangular layout structure. The source area 120 surrounds the body area 150 to constitute an enlarged rectangular layout structure. The gate area 130 separates the drain area 140 and the source area 120.
As mentioned, a conventional power MOS transistor comprises thousands to hundreds of thousands of transistor units. Accordingly, the layout structure of the power MOS transistor 100 comprises a plurality of transistor units disposed side by side in a tight arrangement, wherein the layout structure of each transistor unit is the same as the layout structure of the transistor unit 110. Constrained by its layout structure property, the transistor unit 110 can only provide a limited amount of current. Therefore, to provide a large amount of current, a conventional power MOS transistor requires a huge amount of transistor units, resulting in greatly increased manufacturing cost.
Therefore, there is a need to design a layout structure of a power MOS transistor such that the transistor unit therein can provide a high current, and thus the power MOS transistor can provide a higher current than conventional power MOS transistors, and as a result, the manufacturing costs are reduced.